Electric discharge lamp and starting device therefor



March 25, H. J. MCCARTHY 2,

ELECTRIC DISCHARGE LAMP AND STARTING DEVICE THEREFOR Filed Nov. 8, 1959 I HENRYJNcCARr/l); I

INVENT OR.

ATTORNEY.

Patented 1940 UNITED STATES emails PATENT OFFICE ELECTRIC DISCHARGE AND START- lNG DEVICE THEREFOR 2 Claims. (Cl. 176-124),

The present invention relates to electric gaseous discharge lamps, and in particular to such lamps havingthermionic cathodes and to apparatus for starting and operating such lamps.

An object of the invention is to providean electric gaseous discharge lamp with thermionic cathodes and with apparatus for allowing the cathodes to preheat for a definite interval berore the discharge is started between them. a further object is to provide a switch with the proper time delay to allow preheating of the cathodes under all possible conditions of startin and restarting, and which will not have a deleterious time lag when put into operation for restarting a lamp. A further object is to provide a switch which will start the lamp without a sudden voltage surge.

A feature of the invention is a switch actuated by a bimetallic switch heated by a resistance unit connected between the electrodes of the lamp to be started. A further feature is the use of the diil'erence between starting and operating voltages to allow the switch to be normally open, to close when voltage is applied to the lamp, and to again open after a predetermined cathode heating period to start the lamp.

Other objects, advantages and features oi the invention will lie apparent, from the following description, taken in connection with the aca0 companylng drawing, in which:

Figure 1 is a schematic diagram of the arrangement of apparatus according to the invention;

Figure 2 is a side view of the switching device according to the invention; and

, Figure 3 is a carom-sectional view of part of the same device.

lnl 'lgurehagaseousdischargelamplhas the glass envelope 2 with electrodes 8, 4 at each end. The glass envelope may have an internal 0 coating I of fluorescent material, if desired, and the electrodes 3, 4 may be coils of tungsten wire coated with one or more of the alkaline earth oxides to increase the electron emission, with the auxiliary electrodes 0, I to aid in starting. a An atmosphere of inertgas, such as argon, and also a vapor, such as mercury, may be sealed into the envelope. A lead-in wire 8 from one end of one filament may be connected to one end of the power line from which the device is operated, an end of the other filament may be connected, through a suitable ballast impedance such as the inductance coil II, to the other end 01' the power line by the connection IT. The remaining ends ll, i2 of each filament may be connected together through the resistance i3.

A bimetallic strip is placed close enough .to the resistance iii to be heated by the passageof current therethrough, and is arranged to close the contacts 20, it when it is heated, thereby shortcircuiting the resistance l3 and allowing,

it to 0001.

Figures 2 and 3 show the arrangement oi re sistance and bimetallic strip in more detail. A

graphite, resistance rod I3 is held between the two lead-in strips i8 and I9. Near the middle of the rod 9. bimetallic strip 20 issupported at lead-in wires 24, 25, which pass through the bulb. If the latter is of metal the lead-in wires must, of course, be insulated from the metal.

In operation, when a voltage is placed between I the wires I and II, a current fiows through the resistance I3, heating it, which in time heats the bimetallic strip 20 causing it to expand enough to meet contact it. That short-circuits the resistance II, allowing the latter and strip to cool. In the meantime current through the filaments 2, l, heating them. The resistance It and strip 20 are proportioned so that they cool enough to break the contacts between strip 20 and contact It at about the time the electrodes 3, l are heated, sumciently to start the discharge. The contacts break, placing voltage between the electrodes 4 and 5 and starting the discharge. The

resistance rod l3 should have a high resistance, say 50,000 ohms. For this resistance I have ,ior example used a graphite rod 0.45 inch long and 0.025 inchdiameter.

In order for my circuit to work properly, the lamp must have a gas pressure and electrode spacing, and the tube diameter, such that, when the electrodes are cold, no substantial discharge will pass between the electrodes at the line voltage used. At the instant of connecting my de-' vice to the line, then, no discharge will occur in the lamp but current will pass through the resistance it. This resistance should be high compared to the impedance of the reactance or inductance coil so that practically the entire line voltage will appear across the resistance i3. The passage oi the current through the resistance should be enough to heat the latter sufliciently to transfer enough heat to the bimetallic strip 20 to expand the latter enough to close the contacts, l5, IS. The small current passed through the filament during the period will not be sunlcient to heat it appreciably, so the interval between the connecting of the switch to the line and the closing of the contacts may well be made short; However, the period between the closing of the contacts 20, i6 and the opening of them when the strip 20 has cooled sufficiently to open them must be made long enough, generally at least half a second, to allow the filaments l, 5 to reach the proper electron-emitting temperature.

It will be noted that, on connecting the circuit to the line, no discharge will at first pass between the electrodes in the tube, and practically the entire line voltage will be impressed across resistance l3, heating it and causing the bimetallic strip 20 to close the contacts i5, 16. Closing these contacts short-circuits the resistance, causing it and the bimetallic strip to cool. When they. have cooled sufllciently the contacts will open; and the period in which they remain closed should be adjusted so that the filaments heat up to their proper electron-emitting temperature during that period. Then when the contacts open the discharge will start in the lamp between the heated electrodes.

I'he resistance l3 will again be connected across a voltage, the drop across the lamp, and one might think that it would again heat up and go through its cycle, giving a flashing lamp instead of a smoothly operating one. Such, indeed, might be the case. But in the present invention we take advantage of the fact that the voltage drop across the lamp after starting is less than the drop across the lamp prior to starting. We design the. resistance 53 so that with the full line voltage across it, it is heated enough to close the bimetallic contacts, but so that with the lower lamp operating voltage across it, it does not reach a high enough temperature to close the contacts.

In one lamp with which i. have used the device, for example, the linevoitage was 220 and the lamp operating voltage was only volts. llhere was thus only half the voltage across the resistance aiterstarting that there was before. This would mean that the resistance l3, if contact in value, would only take one-fourth the power while the lamp was operating that it took on starting. However, by using a graphite resistor, which has a negative temperature coelilcient, the ratio can be made even less than one fourth.

In order not to unduly prolong the filament heating period beyond that necessary to reach the proper temperature, an inert gas around the carbon rod is useful to quickly cool the resistor when it is short-circuited. Making the rod of small diameter is also useful in that respect.

The best position for the bimetallic strip is, bent around the middle portion of the carbon rod, since the middle of the rod is hotter than the ends when current flows.

It will be noted that the present switch when operated in my new circuit enables the lamp to be started easily without the damaging shock of a sudden voltage surge, as might be produced by a quick-acting switch of the magnetic or mercury type. If however, a magnetic type switch is desired for any reason it can be used in a manner similar to the present switch by replacing the bimetallic strip by an armature capable of being attracted by the magnet. In such a case, the magnet coil replacing resistor II should have an impedance large compared with that of the impedance l0, and should be such that the line voltage causes the switch to be closed, and yet the operating voltage of the lamp is not sufllcient to close it.

What I claim is:

l.'In combination: an electric gaseous discharge lamp having at least two electrodes, one at least of said electrodes being of the filamentary type; a ballast impedance in series with said lamp; a resistor connecting one end of a filamentary electrode to the other electrode, said resistor having an impedance large compared with that of the ballast impedance; and a bimetallic strip in position to be distorted by the heat developed in said resistor when the latter passes current and to short-*circuit said resistor when distorted sufiiciently.

2. The combination of claim 1 in which: the ballast impedance is such that the operating voltage of the lamp after the electrodes has been heated is much lower than the starting voltage when the electrodes are cold; and in which the resistor connected between the lamp electrodes is positioned so that the heat produced in it by the operating voltage of the lamp is insuihcient to distort the bimetallic strip enough to shortcircuit said resistor, but so that the voltage necessary for short-circuiting is nonetheless below the starting voltage of the lamp when the filament" ary electrode is cold.

my J. McCARTI-IY. 

